1. Field of the Invention
This invention relates generally to injection molding machinery and particularly to locking devices in so-called “two platen” clamp units wherein a movable platen assembly comprises a mold member mounting paten and a clamp force actuator member, the locking devices fixing location of the movable platen assembly for injection when mating mold members are seated.
2. Description of Related Art
In so-called “two platen” clamp units of injection molding machines, it is known to provide a stationary platen for supporting first mold components and a movable platen assembly for supporting second (mating) mold components. The movable platen assembly advantageously comprises a mold member mounting platen for supporting second (mating) mold components and a clamp force actuator member connected to the mold member mounting platen so as to apply clamp force to the mold member mounting platen. In such constructions, it is known to rely on split fixing (“locking”) nuts for releaseably engaging tie bars (also known as “strain rods”) of the clamp unit to fix location of the movable platen assembly relative to the stationary platen for generation of a desired clamp force. Such split locking nuts comprise opposed nut halves movable relative to each other allowing engagement and disengagement of the strain rods. The locking nuts advantageously have internal surface features for engagement with mating external surface features of the strain rods. To fix (“lock”) the movable platen assembly in place when mating mold members are engaged, the nut halves are “closed” so that the internal surface features of the locking nuts engage the external surface features of the strain rods to prevent movement of the nuts longitudinally along the strain rods. The locking nuts abut the movable platen assembly whereby, with the mating mold members engaged, the movable platen assembly is locked in place. With the nut halves “closed” and mating mold components seated, force applied to the mold mounting platen of the moveable platen assembly by the clamp force actuator is transferred through the movable platen assembly and reaction force at the locking nuts is transferred to the strain rods to effect application of a desired clamping force on the mating mold members for injection molding. The aforesaid two platen clamp units customarily have four strain rods and four split locking nuts together with actuators for engaging and disengaging the nut halves with the strain rods. Known constructions of such locking nuts wherein locking nuts are arranged in pairs of two interconnected locking nuts rely on coupling mechanisms to couple motion of one mating nut half to the opposed mating nut half and connecting rods to transfer motion of mating nut halves of a driven (“master”) split locking nut to corresponding mating nut halves of a “slave” split locking nut. Known coupling mechanisms in such arrangements comprise members that engage pins in slots allowing sliding of the pin within the slot with attendant wear and lost motion. Hence, there is a need for improved split locking nut arrangements that overcome deficiencies of known constructions.